1. Field of the Invention
The present invention relates to an apparatus and method for driving and controlling a stepping motor by switching in sequence a plurality of exciting phases in order to control the operating state of an internal combustion engine.
2. Description of the Related Art
Intake air amount of internal combustion engine can be regulated by an intake air amount control apparatus employing a stepping motor drive control in order to drive a stepping motor. The stepping motor is driven as a result of an excitation pattern selected from a plurality of predetermined excitation patterns. The selected excitation patterns are switched in sequence. The direction in which the stepping motor is driven is changed by switching the switching sequence of the selected excitation pattern forwardly or backwardly.
In a conventional intake air amount control apparatus, when an intake air amount regulating valve is opened, the stepping motor is driven forwardly by switching the excitation pattern forwardly for a required number of times. On the other hand, when the intake air amount regulating valve is closed, the stepping motor is driven by switching the excitation pattern backwardly for a required number of times.
Generally, the direction in which the excitation pattern is switched when the stepping motor is being driven, and the number of times the excitation pattern is switched are determined on the basis of the relation between the actual position and the target position of the stepping motor and the difference between these positions.
The target position of the stepping motor is an indicator corresponding to the target opening of the intake air amount regulating valve. The target position of the stepping motor is calculated on the basis of the optimum opening of the intake air amount regulating valve, corresponding to the operating state of the internal combustion engine. The optimum opening is previously stored in the memory.
The actual position of the stepping motor is an indicator corresponding to the actual opening of the intake air amount regulating valve. The actual position of the stepping motor is determined as follows. The position at the time when the initialization is terminated in the stepping motor is assumed as a reference position. Subsequently, the number of times the excitation pattern is switched is summed along the direction in which the excitation pattern is switched. The summation is performed when the stepping motor is driven at the position corresponding to the reference position.
The initialization of the stepping motor is usually performed during key off time when the power supply is stopped. Therefore, an electric current is supplied to the apparatus for driving and controlling the stepping motor for a fixed amount of time after key off. The initialization is performed in the fixed time after the key off. Methods for initializing the stepping motor include a method disclosed in, for example, Japanese Patent Laid-Open No. 57-26238.
Initially, the stepping motor is driven so that the maximum open/close range of the intake air amount regulating valve is exceeded, causing the intake air amount regulating valve to hit a stopper at a maximum drive opening. The position of the stepping motor at this time is assumed as a reference position. Then, the stepping motor is driven so that the actual position of the stepping motor becomes a predetermined target position of the stepping motor during key off. The position of the stepping motor at this time is assumed as a stand-by position. The actual position of the stepping motor is stored in the stepping motor drive control apparatus. After the initialization and the setting of the stand-by position, the power-source relay is turned off, and thus the power to the stepping motor drive control apparatus is shut off.
During key on in which the internal combustion engine is operated, the stepping motor drive control apparatus begins to perform predetermined control on the assumption that the actual position of the stepping motor matches the stand-by position stored in the memory.
However, when, after initialization, power to the stepping motor drive control apparatus is shut off, a microcomputer contained in the stepping motor drive control apparatus is reset. Upon this resetting, the microcomputer outputs a signal of a fixed pattern, and upon receiving this signal, the excitation pattern of the stepping motor becomes a specific pattern. When the excitation pattern at this reset time is different from that when the initialization is terminated, the stepping motor is erroneously driven by the excitation pattern at the reset time.
Therefore, the actual position of the stepping motor during key on does not match the stand-by position stored in the memory and an error occurs, causing a problem that the stepping motor drive control apparatus cannot control the intake air amount regulating valve accurately. As a result, the flow rate of the intake air of the internal combustion engine cannot be adjusted accurately.